With regard to a fuel cell using a polymer electrolyte membrane (hereinafter simply referred to as “electrolyte membrane”) as the electrolyte, an MEGA (membrane electrode and gas diffusion layer assembly) is manufactured by various methods. For example, the MEGA may be manufactured by stacking gas diffusion layers on the respective surfaces of a CCM (catalyst coated membrane) consisting of an electrolyte membrane and catalyst layers or may be manufactured by stacking GDEs (gas diffusion electrodes), each consisting of a catalyst layer and a gas diffusion layer, on the respective surfaces of an electrolyte membrane.
The MEGA of such configuration is thin and is easily bendable. A framed membrane electrode and gas diffusion layer assembly (hereinafter referred to as “MEGA frame”) has accordingly been proposed, in which a frame surrounding the circumference of an MEGA is bonded to and integrated with the circumference of the MEGA with an adhesive. In the MEGA frame, there may be a large gap between the MEGA and the frame, due to the product tolerances of the MEGA and the frame or manufacture tolerance in the course of integrating the frame with the MEGA.
FIGS. 4 and 5 are diagrams illustrating the structure of a conventional MEGA frame. A conventional MEGA frame 100p is manufactured by bonding an MEGA 200 to a frame 300p with an adhesive 400. As shown by a part A in FIG. 4, when a CCM 202 is not covered with the adhesive but is exposed, an electrolyte membrane may be split by repetition of expansion and contraction of the electrolyte membrane. In a fuel cell manufactured by using the MEGA frame 100p having the exposed CCM 202, there may be cross leakage of a reaction gas.
Increasing the amount of the adhesive 400 to prevent the CCM 202 from being exposed may, however, cause the excess adhesive 400 to be spread beyond a gap between the MEGA and the frame as shown in FIG. 5. A broken line H shown in FIG. 5 indicates an extended line of a lower surface of the frame 300p, and an excess adhesive is spread out as illustrated. The spread-out excess adhesive 400 may adhere to a jig to decrease the productivity or may flow into a flow path to increase the pressure loss. This is the problem commonly found in the MEGA manufactured by stacking the GDEs on the respective surfaces of the electrolyte membrane. Japanese Patent Publication (JP) 2005-129343A discloses a MEGA frame including a frame having a space formed for accumulating the adhesive.
The MEGA frame described in JP 2005-129343A employs the structure that an MEGA is placed between two frames and a space for accumulating the excess adhesive is provided to suppress the adhesive from being spread beyond a gap formed at a bonding part of the two frames. As shown in FIG. 4, however, when one frame is bonded to the MEGA with the adhesive, the adhesive may not be guided to the space for accumulating the excess adhesive, even if any, but may be spread out. Accordingly a technique is demanded to reduce the likelihood that the excess adhesive decreases the productivity or increases the pressure loss in the flow path. With regard to the conventional MEGA frame, other needs include cost reduction, resource saving, easy manufacture and improvement of performance.